FIG. 6 is a sectional view showing a configuration of an existing permanent magnet embedded type motor 1. Also, FIG. 7 and FIG. 8 are sectional views showing a configuration of a rotor 2 of the permanent magnet embedded type motor 1. Herein, FIG. 7 shows a state in which a permanent magnet 8 is inserted into a magnet insertion hole 6A or the like, while FIG. 8 shows a state in which the magnet 8 is not inserted into the magnet insertion hole 6A or the like. The permanent magnet embedded type motor 1 includes the rotor 2 and a stator 3 disposed on an outer periphery of the rotor 2. A rotor core 4 configuring the rotor 2 is configured by stacking multiple steel plates formed of a magnetic body. Also, a rotating shaft (not shown) is inserted into a shaft hole 5 formed in the center of the rotor core 4, and fixed using appropriate means such as press fitting or bonding. A coil (not shown) is wound around the stator 3.
Two magnet insertion holes 6A are disposed in the steel plate configuring the rotor core 4, as shown in FIG. 8, drilled so as to spread in a V-shape toward an outer edge 4A of the steel plate. Two cutout holes 7A, extended in a form bending to a d axis side to be described hereafter from each of the magnet insertion holes 6A and communicating with the outer edge 4A of the steel plate, are drilled in positions on the outer edge 4A side that form q axis side end portions to be described hereafter in the two magnet insertion holes 6A disposed in a V-shape.
The two magnet insertion holes 6A and the two cutout holes 7A are provided as a pair, and eight pairs the same as the pair of magnet insertion holes 6A and cutout holes 7A are disposed in the steel plate so as to be distributed evenly. In FIG. 6, the magnet insertion holes of each pair are shown as 6A to 6H, and the cutout holes as 7A to 7H. Consequently, the rotor core 4 is configured by stacking multiple steel plates of identical structures in which eight pairs of the magnet insertion holes 6A to 6H and cutout holes 7A to 7H are drilled.
The permanent magnet 8, which is of a flat plate form configured of a rare earth type magnet such as a neodymium magnet, is inserted into and embedded in the magnet insertion holes 6A to 6H of each pair so that identical poles in each pair oppose each other. The two permanent magnets 8 embedded in the pair of magnet insertion holes 6A configure one pole as a pair, and eight pairs of permanent magnets 8 are embedded in the rotor core 4, whereby eight poles are formed. Not being limited to a rare earth type magnet, another magnet such as an alloy magnet or ferrite magnet may be used as the permanent magnet 8. Also, the permanent magnet 8 may be of a plate form having a curved cross-section in the direction of the axis of rotation. A d axis and q axis are set in this kind of magnet embedded type electric motor, as shown in FIG. 6 to FIG. 8.
The configuration wherein the pair of cutout holes 7A are formed by the pair of magnet insertion holes 6A being extended has an advantage in that magnet flux leakage between the pair of permanent magnets 8 and the neighboring permanent magnets 8 having different magnetic poles is restricted. The configuration wherein the pair of cutout holes 7A bend to the d axis side from the pair of magnet insertion holes 6A and communicate with the outer edge 4A of the steel plate is such that the area of a core region X can be reduced as far as possible in comparison with that of a configuration wherein the pair of cutout holes 7A are formed on an extensions of straight lines from the pair of magnet insertion holes 6A. Therefore, the centrifugal force of the core region X is reduced, and stress acting on a center bridge Y, to be described hereafter, can be reduced.
Meanwhile, the core region X divided by the formation of the cutout hole 7A (the same applies to the cutout holes 7B to 7H of the other pairs) is supported by the center bridge Y, which is a core region existing between the pair of magnet insertion holes 6A (the same applies to the magnet insertion holes 6B to 6H of the other pairs). Consequently, stress concentrates in the center bridge Y due to a load accompanying centrifugal force acting on the core region X when the rotor 2 rotates. Therefore, the center bridge Y is formed to have a constant width (dimension in a circumferential direction) that can withstand stress.
According to the existing example, as heretofore described, a permanent magnet embedded type rotating electrical machine that has superior rotor strength, can be manufactured at low cost, and with which a large torque is obtained, can be realized.